The answer is (3) Oxalate.
Chelation is a chemical phenomenon in coordination chemistry where a ligand (a molecule or ion) forms multiple coordinate bonds with a central metal ion. This term is derived from the Greek word "chele," which means "claw," reflecting the way chelating ligands encircle the metal ion. Chelation typically results in the formation of stable, cyclic structures known as chelate complexes.
In the context of your question, the ligand "Oxalate" (C₂O₄²⁻) is a classic example of a chelating ligand. Here's a detailed explanation of why oxalate forms chelate complexes:
1. Bidentate Ligand:
Oxalate is a bidentate ligand, meaning it has two sites with lone pairs of electrons available for coordination. These sites are typically located on the oxygen atoms of the oxalate molecule. The bidentate nature of oxalate allows it to form two coordinate bonds with a central metal ion.
2. Formation of Chelate Complex:
When oxalate coordinates with a metal ion, it forms a chelate complex. This complex is a cyclic structure in which the metal ion is "clawed" or surrounded by the oxalate ligand, creating a stable and well-defined coordination geometry.
3. Enhanced Stability:
Chelate complexes are often more stable than complexes formed with monodentate ligands, which can only form a single coordinate bond with the metal ion. This increased stability arises from the multiple coordinate bonds and the ring structure, which reduces the chances of the ligand or metal ion dissociating.
4. Application:
Chelation has important applications in various fields. For instance, in biological systems, chelating ligands play a crucial role in metal transport and storage. In analytical chemistry, chelation is used in methods like EDTA titrations for determining metal ion concentrations. Chelation therapy is used in medicine to treat heavy metal poisoning.
5. Example of Chelate Complex:
An example of a chelate complex involving oxalate is the formation of a chelate complex with a metal ion like iron (Fe²⁺). In this case, two oxalate ligands coordinate to the iron ion, forming a stable, six-membered ring structure:
\[Fe^{2+} + 2C_2O_4^{2-} \rightarrow [Fe(C_2O_4)_2]^{2-}\]
This chelate complex is highly stable and plays a role in the chemistry of iron and oxalate in various applications.
In summary, oxalate is a bidentate ligand that forms chelate complexes by creating stable cyclic structures around metal ions. Chelation has significant implications in chemistry, biology, and medicine, and understanding the concept of chelation is fundamental in the field of coordination chemistry. |
